This invention relates to a vacuum-forming molding apparatus and, more particularly, to molding apparatus especially adapted to form containers and other items from sheet materials such as plastic. The molded items are of the type which include projections or depressions which would normally cause difficulty in their removal from the mold.
Various methods and apparatus for vacuum forming items having depressions or projections therein have been devised. In the past, the necessity of providing a solid object around which the projection or depression is formed in the item has created a problem of removing the finished vacuum-formed item after molding. In some vacuum-forming apparatus, the mold itself is formed in two or more parts which are physically separated after molding to allow removal of the finished product. Obviously, the necessity of moving the mold parts away from one another creates complex designs and greater expense.
In such molding apparatus which are especially designed to form various items using vacuum, the problem of retaining sufficient vacuum to draw the material around the desired projection presents other problems in addition to that of removing the finished item. In certain prior apparatuses, projections which are movable through the mold walls for insertion upon molding and withdrawal upon removal of the finished item have been presented. With such devices, it has been found necessary to provide a negative pressure around the projections to ensure proper forming of the item. However, the necessity of providing such negative pressure adds complexity and expense to the apparatus. Further, the pressure around the entire mechanism for inserting and withdrawing the projection must be carefully controlled.
A related problem is that of forming a plurality of vacuum-formed items each including a plurality of depressions or projections while maintaining simplicity in the overall molding mechanisms. Such simplicity both increases the useable life of the apparatus and reduces any necessary maintenance.
A solution to the above problems has been found in the present invention. The invention provides an easily maintained, reliable apparatus for vacuum forming sheet material into containers and other molded items including depressions or projections therein while allowing the easy removal of the finished items after the vacuum-forming step. The invention eliminates the need for complex pressure control around the depression-forming members while allowing the simultaneous forming of a plurality of products in several adjacent molds by utilizing centralized, depression-forming mechanisms.